Lithium secondary batteries include a positive electrode and a negative electrode including materials in which lithium intercalation reversibly occurs as positive and negative active materials, and an organic electrolyte or a polymer electrolyte presented between the positive electrode and the negative electrode. The batteries produce and store electric energy by a redox reaction when the lithium ions are intercalated into and deintercalated from the positive electrode and the negative electrode.
Conventionally, lithium metal was used as a negative active material for lithium secondary batteries. However, an explosion can be caused by a short circuit of the battery due to formation of dendrites when using lithium metal. Therefore, carbonaceous materials such as amorphous carbon, crystalline carbon, etc. have been used recently as the negative active material in place of lithium metal.
A chalcogenide compound may be used as a positive active material. For example, composite metal oxides such as LiCoO2, LiMn2O4, LiNiO2, LiNi1-xCoxxO2 (where 0≦x≦1), LiMnO2, etc. have been studied as the chalcogenide compound. Among the positive active materials, Co-based positive active materials such as LiCoO2 are mainly used because the Co-based positive active materials have high electric conductivity, a high battery voltage, and excellent electrode characteristics.